1. Field of the Invention
This invention relates generally to Physical Vapor Deposition (xe2x80x9cPVDxe2x80x9d) systems, and more particularly to an apparatus and method for reducing redeposition in a PVD system.
2. Description of the Background Art
Physical vapor deposition (xe2x80x9cPVDxe2x80x9d) is a well known technique for depositing metal layers onto semiconductor wafers (also referred to herein as xe2x80x9csubstratesxe2x80x9d). These thin metal layers can be used as diffusion barriers, adhesion or seed layers, primary conductors, antireflection coatings, etch stops, etc.
In a conventional Hollow Cathode Magnetron (xe2x80x9cHCMxe2x80x9d), magnetic fields are used to generate a high-density plasma of Argon (xe2x80x9cArxe2x80x9d) or other suitable inert gas and target material within a cathode of the HCM. The magnetic fields are also used to confine the plasma within the HCM. The cathode has a target, such as Tantalum (xe2x80x9cTaxe2x80x9d), Aluminum (xe2x80x9cAlxe2x80x9d), Titanium (xe2x80x9cTixe2x80x9d), or other suitable metal. A power pin supplies a negative potential to the target such that the magnetic fields in combination with the negative potential cause plasma ions to hit the target with high energy, thereby causing target atoms to dislodge from the surface of the target by direct momentum transfer and also creating secondary electrons. These dislodged atoms and ions are then deposited on the semiconductor wafer.
However, due to the magnetic fields inside the HCM, plasma ions do not evenly erode the HCM target. Specifically, in a conventional HCM, the sidewalls of the target are usually eroded more than the top of the target. Once the sidewalls of the target are fully eroded, the target must be replaced, even though the top of the target may have a large amount of metal remaining.
Further, during a conventional PVD process using titanium nitride (xe2x80x9cTiNxe2x80x9d) or tantalum nitride (xe2x80x9cTaNxe2x80x9d) in a HCM, a high magnetic field provides an ideal TiN or TaN layer on the substrate but also causes redeposition of TiN or TaN particles onto the target. Redeposition may be caused by in-flight gas scattering, reflection of the depositing atoms at other surfaces, less-than-unity sticking of the depositing atoms, or even resputtering from other surfaces on the target. Because the redeposited particles are of a high stress nature, the particles may settle on the substrate, thereby damaging the substrate.
In order to prevent redeposition of TiN or TaN particles, the magnetic field within the cathode is adjusted to minimize redepositon area on the top of the target during the TiN or TaN process. However, the adjustment of the magnetic field leads to a less than optimal film layer on the substrate.
Therefore, a new system and method are needed that can form a uniform layer on the substrate, while reducing target particle formation and increasing uniform target erosion.
The present invention relates to an apparatus for forming a uniform film on a substrate in a PVD system, while decreasing particle defects and increasing uniform erosion of the target. In one embodiment, the apparatus comprises a HCM that can operate under dual modes. A first mode produces a high magnetic field in the HCM for producing a uniform film (or deposition layer) on the substrate but may cause uneven target erosion and particle redeposition on the target. A second mode produces a low magnetic field in the HCM for pasting the target, which erodes the top of the target containing the redeposited material, thereby removing the TiN or TaN particles and compensating for the uneven erosion of the target that may have been caused during the high magnetic field mode.
The present invention also provides a method for forming a uniform film on a substrate in a HCM PVD system and pasting a target in the HCM. After injection of Nitrogen and an inert gas, such as Argon, into the HCM, electromagnetic (xe2x80x9cEMxe2x80x9d) coils in the HCM generate a high magnetic field within the cathode of the HCM. The high magnetic field causes Argon plasma ions to strike the target sidewalls, which is made of Ta or Ti or other suitable metal, thereby dislodging target atoms, which then bond with the Nitrogen to form TaN or TiN depending on the target material. The TaN or TiN then deposits on the substrate on a pedestal in the HCM, forming an optimal uniform layer of TaN or TiN. However, some TaN or TiN also redeposits back onto the target. These particles of TaN or TiN can easily deposit on the substrate.
Accordingly, after the EM coils produce the high magnetic field for processing up to 25 wafers at eight seconds per wafer, the Nitrogen is evacuated from the chamber and the EM coils produce a low magnetic field for pasting. During the pasting, the wafer is replaced with a dummy wafer or a protective electrostatic chuck cover (xe2x80x9cPECxe2x80x9d) wafer is placed on top of the pedestal. The pasting lasts approximately 120 seconds and erodes the top of the target that has the majority of the redeposited TaN or TiN, thereby removing the high stress particles that are most likely to get deposited during the PVD process. In addition, the pasting causes further erosion of the top of target, thereby making the target more uniformly eroded.
Accordingly, the system and method advantageously performs PVD onto a wafer, possibly yielding a uniform film on the wafer, increasing uniformity of target erosion and decreasing particle defects.